.\"	$NetBSD: ungetc.3,v 1.10 2010/04/30 05:56:14 jruoho Exp $
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.\" This code is derived from software contributed to Berkeley by
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.\"     @(#)ungetc.3	8.1 (Berkeley) 6/4/93
.\"
.Dd April 30, 2010
.Dt UNGETC 3
.Os
.Sh NAME
.Nm ungetc
.Nd un-get character from input stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft int
.Fn ungetc "int c" "FILE *stream"
.Sh DESCRIPTION
The
.Fn ungetc
function pushes the character
.Fa c
(converted to an unsigned char)
back onto the input stream pointed to by
.Fa stream .
The pushed-backed characters will be returned by subsequent reads on the
stream (in reverse order).
A successful intervening call, using the same stream, to one of the file
positioning functions
.Po
.Xr fseek 3 ,
.Xr fsetpos 3 ,
or
.Xr rewind 3
.Pc
will discard the pushed back characters.
.Pp
One character of push-back is guaranteed,
but as long as there is
sufficient memory, an effectively infinite amount of pushback is allowed.
.Pp
If a character is successfully pushed-back,
the end-of-file indicator for the stream is cleared.
.Sh RETURN VALUES
The
.Fn ungetc
function
returns
the character pushed-back after the conversion, or
.Dv EOF
if the operation fails.
If the value of the argument
.Fa c
character equals
.Dv EOF ,
the operation will fail and the stream will remain unchanged.
.Sh SEE ALSO
.Xr fseek 3 ,
.Xr getc 3 ,
.Xr setvbuf 3
.Sh STANDARDS
The
.Fn ungetc
function conforms to
.St -ansiC
and
.St -p1003.1-2001 .
.Sh HISTORY
An
.Fn ungetc
function appeared in
.At v7 .
